Creating a Kubernetes Cluster with Kubeadm and Containerd: A Comprehensive Step-by-Step Guide

Kubeadm is a tool designed to simplify the process of creating Kubernetes clusters by providing kubeadm init and kubeadm join commands as best-practice "fast paths." - Kubernetes documentation

In this blog, we'll go through the step-by-step process of installing a Kubernetes cluster using Kubeadm.

Prerequisites

Before you begin, ensure you have the following:

1. Ensure you have a compatible Linux host (e.g., Debian-based and Red Hat-based distributions). In this blog, we're using Ubuntu which is a Debian-based OS.

2. At least 2 GB of RAM and 2 CPUs per machine.

3. Full network connectivity between all machines in the cluster.

4. Unique hostname, MAC address, and product_uuid for every node.

5. Ensure all the required ports are open for the control plane and the worker nodes. You can refer to Ports and Protocols or see the screenshot below.

Disable swap on all the nodes.

sudo swapoff -a
# disable swap on startup in /etc/fstab
sudo sed -i '/ swap / s/^/#/' /etc/fstab

Setup container runtime(Containerd)

To run containers in Pods, Kubernetes uses a container runtime. By default, Kubernetes employs the Container Runtime Interface (CRI) to interact with your selected container runtime. Each node needs to have container runtime installed. In this blog, we'll use containerd.

Run these instructions on all the nodes. I am using Ubuntu on all the nodes.

• Enable IPv4 packet forwarding:
  

  # sysctl params required by setup, params persist across reboots
  cat <<EOF | sudo tee /etc/sysctl.d/k8s.conf
  net.ipv4.ip_forward = 1
  EOF
  
  # Apply sysctl params without reboot
  sudo sysctl --system
  

  Run sudo sysctl net.ipv4.ip_forward to verify that net.ipv4.ip_forward is set to 1

• Specify and load the following kernel module dependencies:
  

  cat <<EOF | sudo tee /etc/modules-load.d/k8s.conf
  overlay
  br_netfilter
  EOF
  
  sudo modprobe overlay
  sudo modprobe br_netfilter
  

• Install containerd:

  Add Docker's official GPG key:
  

  sudo apt-get update
  sudo apt-get -y install ca-certificates curl
  sudo install -m 0755 -d /etc/apt/keyrings
  sudo curl -fsSL https://download.docker.com/linux/ubuntu/gpg -o /etc/apt/keyrings/docker.asc
  sudo chmod a+r /etc/apt/keyrings/docker.asc
  

  Add the repository to Apt sources:
  

  echo \
    "deb [arch=$(dpkg --print-architecture) signed-by=/etc/apt/keyrings/docker.asc] https://download.docker.com/linux/ubuntu \
    $(. /etc/os-release && echo "$VERSION_CODENAME") stable" | \
    sudo tee /etc/apt/sources.list.d/docker.list > /dev/null
  

  Install containerd
  

  sudo apt-get update
  sudo apt-get -y install containerd.io
  

  For more details, refer to the Official installation documentation

• Configure systemd cgroup driver for containerd

  First, we need to create a containerd configuration file at the location /etc/containerd/config.toml
  

  sudo mkdir -p /etc/containerd
  sudo containerd config default | sudo tee /etc/containerd/config.toml
  

  Now, we enable the systemd cgroup driver for the CRI in /etc/containerd/config.toml at section [plugins."io.containerd.grpc.v1.cri".containerd.runtimes.runc.options] set SystemCgroup = true

  

  OR we can just run
  

  sudo sed -i "s/SystemdCgroup = false/SystemdCgroup = true/g" "/etc/containerd/config.toml"
  

  Restart containerd
  

  sudo systemctl restart containerd
  

  Containerd should be running, check the status using:
  

  sudo systemctl status containerd
  

Install kubeadm, kubelet and kubectl

Run these commands on all nodes. These instructions are for Kubernetes v1.30.

• Installapt-transport-https, ca-certificates, curl, gpgpackages
  

  sudo apt-get update
  sudo apt-get install -y apt-transport-https ca-certificates curl gpg
  

• Download the public signing key for the Kubernetes package repositories
  

  curl -fsSL https://pkgs.k8s.io/core:/stable:/v1.30/deb/Release.key | sudo gpg --dearmor -o /etc/apt/keyrings/kubernetes-apt-keyring.gpg
  

• Add theaptrepository for Kubernetes 1.30
  

  echo 'deb [signed-by=/etc/apt/keyrings/kubernetes-apt-keyring.gpg] https://pkgs.k8s.io/core:/stable:/v1.30/deb/ /' | sudo tee /etc/apt/sources.list.d/kubernetes.list
  

• Install kubelet, kubeadm and kubectl
  

  sudo apt-get update
  sudo apt-get install -y kubelet kubeadm kubectl
  sudo apt-mark hold kubelet kubeadm kubectl
  

• This is optional, Enable the kubelet service before running kubeadm
  

  sudo systemctl enable --now kubelet
  

Initialize the k8s control plane

Run these instructions only on the control plane node

• kubeadm init

  To initialize the control plane, run the kubeadm init command. You also need to choose a pod network add-on and deploy a Container Network Interface (CNI) so that your Pods can communicate with each other. Cluster DNS (CoreDNS) will not start until a network is installed.

  We will use Calico CNI, so set the --pod-network-cidr=192.168.0.0/16.
  

  sudo kubeadm init --pod-network-cidr=192.168.0.0/16
  

  Now, at the end of the kubeadm init command, you'll see kubeadm join command

  sudo kubeadm join <control-plane-ip>:<control-plane-port> --token <token> --discovery-token-ca-cert-hash <hash> copy it and keep it safe.

• Run the following commands to set kubeconfig to access the cluster using kubectl
  

  mkdir -p $HOME/.kube
  sudo cp -i /etc/kubernetes/admin.conf $HOME/.kube/config
  sudo chown $(id -u):$(id -g) $HOME/.kube/config
  

  Now, check the node using
  

  $ kubectl get nodes
  NAME             STATUS     ROLES           AGE    VERSION
  ip-zzz-zz-z-zz   NotReady   control-plane   114s   v1.30.2
  

  The node is in NotReady state because message: 'container runtime network not ready: NetworkReady=false reason:NetworkPluginNotReady message:Network plugin returns error: cni plugin not initialized' reason: KubeletNotReady . After setting up the CNI, the node should be in a Ready state.

• Set Up a Pod Network

  We must deploy a Container Network Interface (CNI) based Pod network add-on so that Pods can communicate with each other.

  Install the calico operator on the cluster.
  

  kubectl create -f https://raw.githubusercontent.com/projectcalico/calico/v3.28.0/manifests/tigera-operator.yaml
  

  Download the custom resources necessary to configure Calico.
  

  kubectl create -f https://raw.githubusercontent.com/projectcalico/calico/v3.28.0/manifests/custom-resources.yaml
  

  Verify all the Calico pods are in running state.
  

  $ kubectl get pods -n calico-system
  NAME                                       READY   STATUS    RESTARTS   AGE
  calico-kube-controllers-6f459db86d-mg657   1/1     Running   0          3m36s
  calico-node-ctc9q                          1/1     Running   0          3m36s
  calico-typha-774d5fbdb7-s7qsg              1/1     Running   0          3m36s
  csi-node-driver-bblm8                      2/2     Running   0          3m3
  

  Verify that the node is in a running state
  

  $ kubectl get nodes
  NAME             STATUS   ROLES           AGE     VERSION
  ip-xxx-xx-x-xx   Ready    control-plane   2m46s   v1.30.2
  

Join the worker nodes

Ensure containerd, kubeadm, kubectl, and kubelet are installed on all worker nodes, then run sudo kubeadm join <control-plane-ip>:<control-plane-port> --token <token> --discovery-token-ca-cert-hash <hash>, which you can find at the end of the kubeadm init command's output.

Check the cluster state

Run these commands on the control-plane node since the worker nodes do not have the kubeconfig file.

• Check if the worker nodes are joined to the cluster.
  

  $ kubectl get nodes
  NAME               STATUS   ROLES           AGE    VERSION
  ip-xxx-xx-xx-xx    Ready    <none>          9m9s   v1.30.2
  ip-yyy-yy-yy-yy    Ready    <none>          23s    v1.30.2
  ip-zzz-zz-z-zz     Ready    control-plane   27m    v1.30.2
  

  To add a worker role to the worker node we can use kubectl label node <node-name> node-role.kubernetes.io/worker=worker command.
  

  $ kubectl get nodes
  NAME               STATUS   ROLES           AGE     VERSION
  ip-xxx-xx-xx-xx    Ready    worker          12m     v1.30.2
  ip-yyy-yy-yy-yy    Ready    worker          3m51s   v1.30.2
  ip-zzz-zz-z-zz     Ready    control-plane   31m     v1.30.2
  

• Check the workload running on the cluster
  

  $ kubectl get pods -A
  NAMESPACE          NAME                                       READY   STATUS    RESTARTS   AGE
  calico-apiserver   calico-apiserver-6fcb65fbd5-n4wsn          1/1     Running   0          35m
  calico-apiserver   calico-apiserver-6fcb65fbd5-nnggl          1/1     Running   0          35m
  calico-system      calico-kube-controllers-6f459db86d-mg657   1/1     Running   0          35m
  calico-system      calico-node-ctc9q                          1/1     Running   0          35m
  calico-system      calico-node-dmgt2                          1/1     Running   0          18m
  calico-system      calico-node-nw4t5                          1/1     Running   0          9m49s
  calico-system      calico-typha-774d5fbdb7-s7qsg              1/1     Running   0          35m
  calico-system      calico-typha-774d5fbdb7-sxb5c              1/1     Running   0          9m39s
  calico-system      csi-node-driver-bblm8                      2/2     Running   0          35m
  calico-system      csi-node-driver-jk4sz                      2/2     Running   0          18m
  calico-system      csi-node-driver-tbrrj                      2/2     Running   0          9m49s
  kube-system        coredns-7db6d8ff4d-5f7s5                   1/1     Running   0          37m
  kube-system        coredns-7db6d8ff4d-qj9r8                   1/1     Running   0          37m
  kube-system        etcd-ip-zzz-zz-z-zz                        1/1     Running   0          37m
  kube-system        kube-apiserver-ip-zzz-zz-z-zz              1/1     Running   0          37m
  kube-system        kube-controller-manager-ip-zzz-zz-z-zz     1/1     Running   0          37m
  kube-system        kube-proxy-dq8k4                           1/1     Running   0          9m49s
  kube-system        kube-proxy-t2sw9                           1/1     Running   0          18m
  kube-system        kube-proxy-xd6nn                           1/1     Running   0          37m
  kube-system        kube-scheduler-ip-zzz-zz-z-zz              1/1     Running   0          37m
  tigera-operator    tigera-operator-76ff79f7fd-jj4kf           1/1     Running   0          35m
  

Conclusion

Setting up a Kubernetes cluster with Kubeadm involves a clear and structured process. You can create a functional cluster by meeting all prerequisites, configuring the container runtime, and installing Kubernetes components. Using Calico for networking ensures seamless pod communication. With the control plane and worker nodes properly configured and joined, you can efficiently manage and deploy workloads across your Kubernetes cluster.

Thank you for reading this blog; your interest is greatly appreciated, and I hope it helps you on your Kubernetes journey; in the next article, we'll explore running workloads in the Kubernetes cluster.